High efficiency power generation system and system upgrades

ABSTRACT

A power generation system includes an inert gas power source, a thermal/electrical power converter and a power plant. The thermal/electrical power converter includes a compressor with an output coupled to an input of the inert gas power source. The power plant has an input coupled in series with an output of the thermal/electrical power converter. The thermal/electrical power converter and the power plant are configured to serially convert thermal power produced at an output of the inert gas power source into electricity. The thermal/electrical power converter includes an inert gas reservoir tank coupled to an input of the compressor via a reservoir tank control valve and to the output of the compressor via another reservoir tank control valve. The reservoir tank control valve and the another reservoir tank control valve are configured to regulate a temperature of the output of the thermal/electrical power converter.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/742,760, entitled “High Efficiency Power Generation Systemand System Upgrades,” filed Jun. 18, 2015, which is a continuation ofU.S. patent application Ser. No. 14/451,863, entitled “High EfficiencyPower Generation System and System Upgrades”, now U.S. Pat. No.9,068,468, issued Jun. 30, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/971,273, entitled “High Efficiency PowerGeneration System and System Upgrades,” now U.S. Pat. No. 8,826,639,issued Sep. 9, 2014, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/691,955, entitled “HiEff Mod.” filed on Aug. 22,2012, which applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention is directed, in general, to power generationsystems and, more specifically, to a system and method for employing aBrayton closed-cycle power generator to produce electricity and providea thermal source for a thermally driven load.

BACKGROUND

Burning coal to produce electrical power is one of the critical 21^(st)century power generation dilemmas. Fifty-five percent of global powercomes from burning coal. The resulting flue gas emissions from burningcoal contain a broad spectrum of intractable climate-change andhealth-compromising compounds. For instance, carbon dioxide, a climatechanging gas, is virtually impossible to economically eliminate inpower-generating facilities. The use of natural gas instead of coalreduces, but does not eliminate the carbon dioxide. Both coal andnatural gas also discharge ozone-producing gasses and soot particulates,which are costly to extract from exhaust and flue gas.

Natural gas infrastructure for domestic space and water heating is fullydeveloped as a preferred fuel source. It is advantageous for groundtransportation and as feedstock for a broad range of chemicalprocessing. The available natural gas stores, however, are much morelimited than coal. The use of natural gas for electrical powergeneration appears to be misguided in the long term.

To provide a perspective, the Tennessee Valley Authority (“TVA”)Kingston Fossil Plant, burns about 14,000 tons of coal a day, butproduces over 50,000 tons of carbon dioxide per day. Their discharge ofozone and particulate emissions is not stated. This plant powers 700,000homes, but requires daily delivery of 140 freight-car loads of coal thatmust be dug out of the ground and transported to Kingston. Coalextraction, cross country delivery, on site handling and burning can bedirectly related to human costs, and can be directly related to mountingenvironmental degradation for just this one plant.

About twenty percent of world power is produced from water-coolednuclear fission with varying degrees of public acceptance, from passivebut reluctant acceptance to hysterical fear and absolute demands fornuclear power elimination. Existing nuclear power plants provideinherent risks, but are engineered and operated to exceptional safetystandards. Nuclear power plants were originally designed for a 20-yearlife. An increasing number of nuclear plants are approaching an age of60 years. Ten- and 20-year operating license extensions have beenrepeatedly granted after comprehensive examinations and analysis.Satisfying solutions to plant aging are elusive.

Population growth, rising standards of living and economic growth areputting world-wide electrical grid generating capacity margins at risk.Conservation and alternative generating sources are helpful, but are notexpected to meet the growing demand. In addition, electrical demandgrowth to power the growing worldwide demand for air conditioning andthe anticipated demand for electric cars are projected to further overstress the capacity of existing grids. Clearly, there is a growingdemand for more electrical power, but current methods of powergeneration are problematic and unsustainable.

In 1824, Sadi Carnot described the ultimate heat engine efficiency limitof a perfect engine dependent on the highest heat-input temperature andthe lowest waste-heat rejection temperature. Rankine, Diesel, Otto andBrayton conceived basic power-generation engine cycles and others haverefined these basic engines. The Atkinson cycle is a recent improvementof the Otto and Diesel cycles. General Electric (“GE”) and Siemens havedeveloped open gas turbine/steam combined-cycle power plants. Each hasmade unique contributions to power production technology.

Steam-based Rankine cycle engines dominate electric power generation. ARankine-cycle engine has two possible energy sources, burning coal orother fossil fuels, and nuclear fission. In both, superheated steam athigh pressure drives a turbine that in turn drives an electricalalternator. A steady, continuous, recirculating flow of water and steamflows through a boiler, turbine, condenser and water pump in this closedsystem. The heat source is external combustion of coal, sub-gradehydrocarbons or natural gas, or from a boiling-water nuclear reactor.Waste heat is rejected from the turbine exhaust at or near ambientdew-point temperatures in a steam-condensing heat exchanger. This lowtemperature waste heat rejection temperature is key to normal cycleefficiencies in the 35 percent (“%”) to 40% range. However, thecontinuous, superheated, steam turbine inlet temperature is limited toabout 1000 degrees (“°”) Fahrenheit (“F”) to avoid hydrogenembrittlement of the turbine blades. This material limitation precludeshigher efficiencies from operating at higher superheated steamtemperatures. This superheated steam temperature limit exists for bothcombustion and nuclear heat sources.

Coal-fired units produce electricity by burning coal in a boiler to heatwater to produce steam, generally employing a coal/fossil fueled, closedRankine cycle (steam) power plant. Steam, at tremendous pressure, flowsinto a turbine, which spins a generator to produce electricity. Thesteam is cooled, condensed back into water, and the water is pumped backto the boiler to continue the process.

For example, the coal-fired boilers at TVA's Kingston Fossil Plant nearKnoxville, Tenn., heat water to about 1000° F. (540° Celsius (“C”)) tocreate steam. The steam is piped to turbines at pressures of more than1,800 pounds per square inch (130 kilograms per square centimeter). Theturbines are connected to the generators and spin them at 3600revolutions per minute to make alternating current electricity at, e.g.,20,000 volts. River water is pumped through tubes in a condenser to cooland condense the steam discharging from the turbines. The Kingston plantgenerates about 10 billion kilowatt-hours a year, or enough electricityto supply 700,000 homes. As mentioned previously hereinabove, to meetthis demand Kingston burns about 14,000 tons of coal day, an amount thatwould fill 140 railroad cars daily.

The open Brayton cycle is generally used in gas turbine andcombined-cycle power plants that burn liquid or gaseous fossil fuels,and produce refractory environmental stressors. The turbine blades andother structures formed of superalloy materials to limit oxidation andcreep temperature properties, however, limit turbine operatingtemperatures to about 2000° to 2100° F. Complex internal turbine bladecooling systems enable turbine inlet gas temperatures to exceed 2500°F., but these high temperatures produce a full range of harmful ozoneactivators and high levels of nitrous and nitric oxides (“NOx”). Typicalturbine exhaust temperatures of 500° to 700° F. compromise efficiency tomid-40 percent range. In conventional fossil-fueled power plants,whether designed for steam or gas turbines, the combustion products areozone-producing gases, carbon dioxide, and particulate soot that areenvironmental stressors. These toxic exhaust products cannot be easilyeliminated, and are costly to reduce. Climate stability-challengingcarbon dioxide removal from coal fired boilers is not practical at thistime.

In nuclear powered power-generating plants, high-pressure steam isproduced by contact cooling of water with fission-reacting fuel rods. Inthe heating process, the circulating water and steam become radioactive.This large mass of radioactively contaminated water is an unavoidableand an unfortunate side effect in all existing nuclear power plants.Consequently, all existing nuclear plants must absolutely prevent waterand steam venting or leakage. They must also be actively controlled inall operating modes to prevent “melt down” and accompanying waterdissociation, hydrogen explosions, and uncontrolled spread ofradioactive gases, liquids, and particles. Prevention of these types offailures is a high tribute to comprehensive and exhaustive excellence inengineering, manufacturing, and vigilant operation in a safety culture.

Notwithstanding these precautions, three reactor meltdowns have happenedin the past half century including Three Mile Island without injuries.Another incident occurred at Chernobyl with 31 on-site deaths andlong-term evacuation of a 1000 square mile region, plus undisclosed,high human and animal sickness and early deaths. In 2011, multiple meltdowns at the Japanese Fukushima power plants followed a tsunami withmonumental tragedies.

Limitations of conventional power generation approaches have now becomesubstantial hindrances for wide-scale power generation with highefficiency and low levels of undesirable environmental pollutants. Nosatisfactory strategy has emerged to provide a sustainable, long-termsolution for these issues. Accordingly, what is needed in the art is anew approach that overcomes the deficiencies in the current solutions.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by advantageous embodimentsof the present invention, in which a power generation system includes aninert gas power source, a thermal/electrical power converter and a powerplant. The inert gas power source is formed with an input and an output.The thermal/electrical power converter includes a compressor with anoutput coupled to the input of the inert gas power source. The powerplant has an input coupled in series with an output of thethermal/electrical power converter. The thermal/electrical powerconverter and the power plant are configured to serially convert thermalpower produced at the output of the inert gas power source intoelectricity. The thermal/electrical power converter includes an inertgas reservoir tank coupled to an input of the compressor via a reservoirtank control valve and to the output of the compressor via anotherreservoir tank control valve. The reservoir tank control valve and theanother reservoir tank control valve are configured to regulate atemperature and/or pressure of the output of the thermal/electricalpower converter.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIGS. 1 and 2 illustrate diagrams of embodiments of power generationsystems;

FIG. 3 illustrates a diagram of an embodiment of a heat exchanger of apower generation system;

FIG. 4 illustrates an elevation view of an embodiment of an inert gaspower source;

FIG. 5 illustrates a flow diagram of an embodiment of a method forproviding power for a thermally-driven process load;

FIGS. 6 and 7 illustrate diagrams of embodiments of power generationsystems; and

FIG. 8 illustrates a flow diagram of an embodiment of a method forconstructing a thermal/electrical power system.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated, and may not beredescribed in the interest of brevity after the first instance. TheFIGUREs are drawn to illustrate the relevant aspects of exemplaryembodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and usage of the present exemplary embodiments are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the systems,subsystems and modules associated with a process for producing a thermalpower source.

Combined gas/steam cycle power generation employing open Brayton-closedRankine combined cycles includes both fuel-burning gas turbine andfuel-burning steam turbine generators. Hot turbine exhaust energy isrecovered in a boiler to partially generate steam and superheated steamof a steam power plant. A combined-cycle power generation arrangement,however, requires a full complement of complex and costly components andcontrols, with full facility costs of both a high performance gasturbine and a complete steam power plant. There remains a complex andbroad range of ultra-high temperature combustion and environmentalstressors that offset or diminish some of the value of combined-cyclepower generation arrangements.

U.S. Pat. No. 5,431,016, entitled “A High Efficiency Power Generation,”to W. E. Simpkin, issued Jul. 11, 1995, (hereinafter “Simpkin 1”), whichis incorporated herein by reference, describes a power generating systemformed with a light gas reactor powered by a closed Brayton cycle thatdischarges waste heat to supply energy for a steam-based Rankine cycle.The physical application is directed to specifying carbon-carbonmaterials in all ultra-high temperature locations. Simpkin 1 employs anultra-high temperature light gas to benefit from energy efficiencyadvantages of the two cycles while reducing limitations of each. Simpkin1 is an advance using Carnot's principles to produce higher efficiencypower generation. A holistic approach is described that enhancesoverall, compound-cycle efficiency.

Simpkin 1 also includes design concepts for piping and pressure vesselscontaining very high temperatures within a conventional steel structure.A portion of Simpkin 1 was issued later as U.S. Pat. No. 5,896,895,entitled “Radiation Convection Conduction Heat Flow InsulationBarriers,” to W. E. Simpkin, issued Apr. 27, 1999, (hereinafter “Simpkin2”), which is incorporated herein by reference. The original insulationconcept is retained in the “High Efficiency Power Generation”descriptions disclosed in Simpkin 1.

Light gas (e.g., helium, “He”) reactors are generally referred to asGeneration IV Emerging Nuclear Power Reactors, which have a longResearch and Development (“R&D”) history motivated by inherent safetyaspects. Helium is a unique, totally stable gas at all pressures andtemperatures encountered in the reactor designs. Helium does not becomeradioactive, even in high intensity radiation or at very hightemperatures. It does not change state and is absolutely inert. Heliumdoes not interact chemically with organic or inorganic atoms ormolecules. Its inertness is absolute even to surface effects. Heliumdoes not ionize at temperatures encountered in reactor-coolingapplications and does not change its atomic structure.

Advanced nuclear technology is globally coordinated by the Generation IVInternational Forum. Two of the six Generation IV nuclear reactordevelopment programs are helium cooled. The Very High TemperatureReactor (“VHTR”) is a thermal reactor in full scale prototype build in2013, and the Gas Cooled Fast Neutron Breeder Reactor (“GFR”) nowundergoing component testing and development is seven to ten years laterfor deployment than the VHTR. These two helium-cooled reactors aresignificantly different in their neutron action processes and lifecycles. As producers of very high temperature helium flows, they arequite similar. Applications using the VHTR and the GFR are describedherein as functionally interchangeable for providing a thermal source ofvery high temperature helium.

The GFR has been projected to beneficially reduce the difficult andcostly nuclear waste storage problem. Existing nuclear waste couldprovide a very low cost fuel supply for decades, if not centuries, inGFR power production. The GFR is a fast neutron breeder reactor thatextracts nearly all of the potentially fissionable material, leavinglow-level residual radiation waste. Fourth Generation nuclear powerplants include helium-cooled (light gas) reactors because they areinherently safer and environmentally benign. A thermal-version VHTR anda GFR provide probable further growth potential beyond today's highperformance for both reactors.

The VHTR is a graphite-moderated, helium-cooled reactor with a thermalneutron spectrum. The VHTR is designed to be a high-efficiency system,which can supply electricity and process heat to a broad spectrum ofhigh-temperature and energy-intensive processes. A U.S. Department ofEnergy (“DOE”) reference reactor formed with a 600 megawatt thermal(“MWth”) core connected to an intermediate heat exchanger can deliverprocess heat, e.g., up to 900° C. (1652° F.). The reactor core can be aprismatic block core or a pebble-bed core according to a structure ofthe fuel particles. Fuel particles are coated with successive materiallayers that are high-temperature resistant, and are then formed eitherinto fuel compacts or rods that are embedded into hexagonal graphiteblocks for a prismatic block-type core reactor, or are formed intographite coated pebbles for a pebble-bed core. The reactor produces heatwith core outlet helium temperatures up to about 1000° C. The closedhelium circuit can enable non-power producing applications such ashydrogen production or process heat for the petrochemical industry.Thermal processes requiring lower temperature than that supplied by areactor supply could be configured to supply an application-specificcompressor-turbine-generator set providing an application-specifiedturbine discharge temperature. As an application of a nuclearheat-generating process, hydrogen can be efficiently produced from onlyheat and water by using a thermochemical iodine-sulfur process, or ahigh temperature electrolysis process, with additional natural gas, byapplying a steam-reformer technology. A prototype VHTR is beingfabricated in 2013 for demonstration trials in the mid-2010s, andcomponent and sub-system testing have demonstrated inherent safetycharacteristics of a GFR.

Thus, a VHTR offers a thermal source for high-efficiency electricityproduction and a broad range of process heat applications whileretaining desirable safety characteristics in normal as well asoff-normal events. The basic technology for the VHTR has been wellestablished in former high temperature gas reactor plants such as theUnited States Fort Saint Vrain and Peach Bottom prototypes, and theGerman AVR and THTR prototypes. The technology is being advanced throughnear- or medium-term projects lead by several plant vendors and nationallaboratories, such as PBMR, GTHTR300C, ANTARES, NHDD, GT-MHR, and NGNPin South Africa, Japan, France, Republic of Korea, and the UnitedStates. Experimental reactors such as the HTTR in Japan (30 MWth) andthe HTR-10 in China (10 MWth) support advanced concept development, aswell as cogeneration of electricity and nuclear heat productionapplications.

The GFR system employs a fast-neutron spectrum, helium-cooled reactorand a closed fuel cycle. The DOE Generation IV GFR demonstration projectuses a direct-cycle helium turbine for electricity generation, or canoptionally use its process heat for production of hydrogen. Through thecombination of a fast neutron spectrum and full recycling of actinides,the GFR reduces the production of long-lived radioactive waste. The fastneutron spectrum of the GFR also makes it possible to use availablefissile and fertile materials (including depleted uranium) much moreefficiently than thermal spectrum gas reactors that employ once-throughfuel cycles. Several fuel forms are candidates that hold the potentialfor operating at very high temperatures and ensure excellent retentionof fission products. The fuel forms include composite ceramic fuel,advanced fuel particles, or ceramic-clad elements of actinide compounds.Core configurations can be based on pin- or plate-based assemblies or onprismatic blocks. A DOE Generation IV GFR reference cites an integratedon-site “nuclear waste” refabrication plant GFR fuel supply. Through thecombination of a fast neutron spectrum and full recycling of actinides,the GFR develops very low-cost power and reduces the production oflong-lived radioactive waste.

As introduced herein, a compound electrical power generator is formedhaving two interdependent closed-cycle turbine-driven alternators. Aclosed-cycle Brayton inert (e.g., helium) gas turbine/alternator powergeneration system is coupled to and supplies superheated steam to aclosed-cycle Rankine steam turbine/generator. An overhauled candidate, aretired or new Rankine steam turbine/generator, is employed for theRankine power-generation process. The Rankine steam turbine/generatorreceives steam at controlled quantities, pressure, and temperature fromenergy extracted from heat exchangers from high temperature, heliumturbine outflow gas produced by the Brayton power generation system. ABrayton-cycle gas turbine is powered by an inert light gas reactor(e.g., a VHTR or GFR). The steam temperature supplied to the Rankinesteam turbine/generator system is set and controlled to anapplication-dependent temperature level sufficient to power the Rankinesteam turbine/generator load.

The turbine employed in the Brayton power generation system has a low,tailored pressure ratio, and a low-cost compressor and gas turbine.Thus, the Brayton power generation system produces power and providessuperheated steam according to specification for integration into anexisting steam turbine generator to form a compound power plant. In anembodiment, the Brayton power generation system provides power for athermally driven chemical or refining process such as hydrogenproduction or petroleum refining. Such chemical or refining process canbe endothermic or exothermic.

The power-generation architectures introduced herein come at a time intechnology development in which safety, health, and environmentalfactors are of greater consequence than achieving record systemefficiencies. Profound advances in health and safety, and elimination ofenvironmental stressors can be achieved with described modifications ofan existing utility power plant. In addition, the modificationsintroduced herein can readily increase existing plant capacities by 40%or more, with potential for further capacity growth.

The power generation modifications are equally suitable for eitherfossil-fuel fired or nuclear power plants. The heat source system andboiler of an existing fossil-fueled or nuclear power plant would beremoved. The remainder of the plant, steam turbine, alternator,condenser, pumps, and electrical- and control-system elements continuein use as before.

Additional large economic savings come from using the same site, thesame electrical distribution system, the same support and physicalinfrastructure, and unchanged cooling water supply and steam condensersystems. As introduced herein, modifications of a steam generatorprovide a large increase in compound plant capacity and efficiency.Re-fabricated “nuclear waste” can provide an abundant supply of low-costfuel for the GFR. These economic leverages provide incentives forimplementing a high efficiency modification of a moth-balled plant or inlieu of a necessary major overhaul.

A modified power plant can provide substantial financial benefits to autility. Valuable assets can be reclaimed, including the site, rotatingsystems, cooling condensing system, electrical infrastructure/gridconnections, and functional elements of the business infrastructure.Thus, a substantial plant capacity increase can be obtained that usesabundant, low-cost fuel, thereby providing a safer and cleanerpower-generation solution than previously employed.

Turning now to FIG. 1, illustrated is a diagram of an embodiment of apower generation system. The power generation system includes two,interdependent, closed-loop thermal/electrical power systems with aBrayton closed-loop power generation and processing system, and aRankine closed-loop power processing system. The elements illustrated inFIG. 1 are not drawn to scale.

A thermal/electrical power converter 102 is formed with a generator(such as an alternator) 110, a gas turbine 112, and a compressor 114,all mechanically coupled via a rotatable shaft 130. An electrical poweroutput 111 of the generator 110 may be coupled through switchgear and anoptional power converter 113 to a power grid 106, such as an alternatingcurrent (“ac”) or a direct current (“dc”) power grid. The generator 110is an electro-mechanical device that can produce either an ac output ora dc output according to its design. The term “alternator” will be usedherein to refer to an electro-mechanical device that can produce an acoutput. The switchgear and an optional power converter 113 may includean ac transformer and an inverter.

In an embodiment, the optional power converter 113 can be employed toconvert a dc output of the generator 110 to ac at a frequency suitablefor connection to the power grid 106. In an embodiment, the optionalpower converter 113 can be employed to convert an ac output of thegenerator 110 at one frequency to another frequency suitable forconnection to the power grid 106. An optional gear box may be coupledbetween the gas turbine 112 and the generator 110 to provide a differentrotation rate of the generator 110 relative to that of the gas turbine112.

An input 124 of the gas turbine 112 is coupled to a high-temperature,high-pressure, inert gas thermal power source (referred to as an “inertgas power source” or “inert gas thermal power source”) 101, such as aVHTR or GFR helium-cooled, light gas reactor. An examplehigh-temperature, high-pressure helium cooled gas power source isillustrated and described hereinbelow with reference to FIG. 4. Otherinert gases such as, without limitation, argon, xenon, and neon, arecontemplated within the broad scope of the present invention as aheat-transfer/working fluid medium for an inert gas power source. Alow-pressure output 128 of the gas turbine 112 is coupled to ahigh-temperature input 129 of a heat exchanger 140. A low-pressureoutput 126 of the heat exchanger 140 is coupled to a low-pressure input123 of the compressor 114. A high-pressure output 121 of the compressor114 is coupled to an input of the inert gas power source 101 via returnline 122.

An inert gas reactor such as a VHTR or a GFR can introduce dustparticles into the inert gas flow, particularly with a pebble-bedreactor. Over time, dust particles can erode gas turbine and compressorblades, and even inert gas piping at piping bends. To remove such dustparticles from the inert gas flow, a filter 131 can be installed betweenthe low-pressure output 126 of the heat exchanger 140 and thelow-pressure input 123 of the compressor 114, which is a low temperatureposition to install a filter 131. In an embodiment, such filter 131 canhave a minimum equivalent reporting value (“MERV”) of 7.

The thermal/electrical power converter 102 is assumed herein to beoperable between its input and a combined output that includes theelectrical power output 111 of the generator 110 and a thermal outputbetween a high-temperature steam output 142 and a low-temperature,liquid-water input 144 of the heat exchanger 140 with very highlyefficient power conversion. This assumes that the generator 110 isoperable with substantially 100% power conversion efficiency. Apractical generator operable to convert mechanical shaft power to anelectrical output in a high-power plant can generally achieve a powerconversion efficiency in the mid- to high-90% range, and the slightlyimperfect power conversion efficiency of such a high-power generator isignored herein. Such mechanical-to-electrical power conversion plantsare not limited by a second-law efficiency constraint imposed by aCarnot cycle.

The high-temperature steam output 142 of the heat exchanger 140 iscoupled to an input 143 of a thermally driven Rankine-cycle power plant(also referred to as a “power plant”) 104. In an embodiment, the thermalenergy produced at the high-temperature steam output 142 of the heatexchanger 140 provides the power input to the power plant 104, which canbe an existing, modified steam-driven plant. A high-pressure,cooled-water output 145 of the power plant 104 is coupled to thelow-temperature, liquid-water input 144 of the heat exchanger 140. Thus,substantially the entire thermal output of thermal/electrical powerconverter 102 is supplied to the power plant 104, with exception of thesmall inefficiency of the generator 110. No substantial thermal sinkneed be coupled to the thermal/electrical power converter 102 withexception of modest cooling for the generator 110.

Pipeline pressure losses are included in calculating heat exchangerpressure drops for convenience in calculating system performanceevaluations. A small pressure drop at the input side of the heatexchanger 140 does not contribute to system inefficiency. The smallpressure drop of the heat exchanger 140 is simply accommodated byoperating pressure differences between the compressor 114 and the gasturbine 112. Thermal content of heated water or other heated fluid thatmay be employed to cool the generator 110 (or other system elements) maybe employed to preheat the low pressure, cooled helium at thehigh-temperature steam output 142 of the heat exchanger 140 before beingsupplied to the compressor 114 to provide a further efficiencyenhancement to the thermal/electrical power converter 102.

The power plant 104 is operable in a conventional way. High-pressure,high-temperature steam from the high-temperature steam output 142 of theheat exchanger 140 is coupled to a high-pressure, high-temperature inputof a gas turbine 152 of the power plant 104. A generator 150 of thepower plant 104 is mechanically coupled to a rotatable shaft of the gasturbine 152, and an electrical power output 151 of the generator 150 maybe coupled to the power grid 106 through a switchgear and an optionalpower converter 153 that may be similar in function to the switchgearand optional power converter 113 described previously hereinabove. Thepower grid to which the generator 150 is coupled can be the same ordifferent power grid to which the generator 110 of thethermal/electrical power converter 102 is coupled.

A low-pressure, steam output 154 of the gas turbine 152 is coupled to aninput of a heat exchanger/condenser 156 of the power plant 104. Alow-temperature output 155 of the heat exchanger/condenser 156conducting low-pressure, cooled water is coupled to a low-pressure inputof a water pump 160 of the power plant 104. A high-pressure water outputof the water pump 160 is coupled to the low-temperature, liquid-waterinput 144 of the heat exchanger 140. A high-temperature water output 158of the heat exchanger/condenser 156 is coupled to a low-temperaturethermal sink such as cooling water supplied from a river. Alow-temperature (e.g., 40 to 80° F.) liquid-water input 159 of the heatexchanger/condenser 156 is coupled to the low-temperature thermal sink.The heat exchanger/condenser 156 can be an unchanged steam condenser forwaste heat rejection to a cooling water subsystem in a thermally-drivenprocess.

In a manner similar to that described hereinabove for the helium filter131 installed after the low-pressure output 126 of the heat exchanger140, a water filter can be introduced into the cold water return betweenthe heat exchanger/condenser 156 and the heat exchanger 140 to removesuspended particles.

The overall power-conversion efficiency of the power generation systemillustrated in FIG. 1 is the summed electrical outputs of the generators110, 150 divided by the thermal input measured between the input 124 ofthe gas turbine 112 and the high-pressure output 121 of the compressor114 (to the inert gas power source 101), and can be of the order of 45to 50% or more in a practical plant. The overall thermal efficiency of atypical nuclear-, natural gas-, oil-, or coal-fueled power plant istypically in the mid-thirties percent, and is limited by the Carnotefficiency of practical Rankine cycle gas turbine/compressor powerconverters. Overall efficiency of a front-end thermal/electrical powerconverter 102 as introduced herein is not so limited.

In an example embodiment, the inert gas power source 101 provides aninert gas thermal source at a temperature of about 1650° F. with anenergy flow of about 1100 MWth to the input 124 of the gas turbine 112.It is contemplated that the inert gas power source 101 can produce aninert gas at a temperature as high as 2500° F. or more (1650° F. in anexample), and that left-over thermal energy at a lower temperatureproduced by the inert gas power source 101 can be fully utilized topower a thermally driven, closed-loop, Rankine cycle steam power systemor other thermally powered process such as, for example, a chemicalreactor that produces gaseous hydrogen. The shaft output power in thisexample of the gas turbine 112 is about 230 thermal megawatts (“MWth”),which is assumed for this example to be converted with 100% efficiencyto about 230 electrical megawatts (“MWe”). The heat exchanger 140produces about 870 MWth, which is the difference between the 1100 MWthproduced by the inert gas power source 101 and the 230 MWe produced bythe generator 110.

It is also contemplated that efficient gas turbine-compressor-generatorsets will rotate at controlled rotational speeds of 20,000 revolutionsper minute or more. It is further contemplated that gas turbine bladesformed of carbon-carbon composite materials or superalloys such asHastelloy, Inconel, Waspaloy, and Rene alloys will be able to sustainsuch rotational speeds at temperatures as high as 2800° F. Nonetheless,a practical highly efficient thermal/electrical power converter plantcan be formed with lower rotational speeds and lower operatingtemperatures.

The low-pressure output 128 of the gas turbine 112 is regulated to atemperature of about 960° F. by controlling the amount of inert gas inthe inert gas power source 101 with a first reservoir tank control valve117 and a second reservoir tank control valve 118, each reservoir tankcontrol valve coupled to and in series with an inert gas (e.g., helium)reservoir tank (also referred to as a “reservoir tank”) 116. Thereservoir tank 116 provides a thermal sizing function for matching thehelium mass flow in the thermal/electrical power converter 102 to thethermal power requirement of the thermally driven process load coupledthereto, which can be an existing, functioning system that waspreviously powered by a carbon combustion-based or a nuclear power-basedpower source. The reservoir tank 116 is coupled to the low-pressureinput 123 of the compressor 114 via the first reservoir tank controlvalve 117 and the high-pressure output 121 of the compressor 114 via thesecond reservoir tank control valve 118 and is configured to regulate apower output and/or a temperature of the inert gas power source 101and/or the thermal/electrical power converter 102.

As an example, if a 900 MWe steam plant is supported by three manifoldedthermal/electrical power converters 102, the helium supply for eachprovided by the reservoir tank 116 would be “vernier” trimmed employingrespective first and second reservoir tank control valves 117, 118 forsubstantially perfect load sharing while providing a specifiedtemperature at the output 128 of the gas turbine 112. In a variableturbine speed plant that provides a dc output, the first and secondreservoir tank control valves 117, 118 could be employed to vary thetemperature or the output power at the output 128 of the gas turbine112. In a system employing a fixed rotation rate for the gas turbine112, the first and second reservoir tank control valves 117, 118 couldbe employed for load following. This is unique because all systemtemperatures would be fixed and part load efficiency would be asubstantially invariant over a range of the electrical load coupled tothe system.

In an embodiment, the gas turbine 112 is operated at substantially aconstant speed of rotation so that the generator 110 coupled to therotatable shaft 130 of the gas turbine 112 can produce an ac output at asubstantially fixed frequency (e.g., 60 Hertz (“Hz”)). A temperature ofthe low-pressure cooled helium coupled to the low-pressure input 123 ofthe compressor 114 is about 100° F. The first reservoir tank controlvalve 117 is coupled to the low-pressure output 126 of the heatexchanger 140. The second reservoir tank control valve 118 is coupled tothe return line 122 from the high-pressure output 121 of the compressor114. Pressure of the helium gas in the reservoir tank 116 isintermediate between the helium pressure at the low-pressure input 123to the compressor 114 and the helium pressure at the high-pressureoutput 121 of the compressor 114. By opening the first reservoir tankcontrol valve 117, helium from reservoir tank 116 flows into theclosed-cycle helium loop that supplies the inert gas power source 101,thereby increasing the overall helium pressure in the closed-cyclehelium loop. By opening the second reservoir tank control valve 118,helium is returned to the reservoir tank 116 from the return line 122,thereby decreasing the overall helium pressure in the closed-cyclehelium loop. In this manner, temperature of helium output flow from theinert gas power source 101 is controlled.

In an example system, the high-pressure, high-temperature steam producedat the high-temperature steam output 142 of the heat exchanger 140 isabout 900° F. The high-pressure steam supplied to the input of the gasturbine 152 is reduced by the gas turbine 152 to low-pressure steam at atemperature of about 80 to 100° F. at the low-pressure, steam output 154of the gas turbine 152. The generator 150 is mechanically coupled to therotatable shaft of the gas turbine 152 and produces 300 MWe. Theremaining thermal output is transferred to the thermal sink (i.e.,cooling water supplied from a river or other substantial body of water).The low-pressure steam at the low-pressure, steam output 154 of the gasturbine 152 is condensed to low-pressure water of about the sametemperature in the heat exchanger/condenser 156. The water pump 160repressurizes the water at its output at substantially the sametemperature.

The overall compound system efficiency of the power generation systemperformed by the thermal/electrical power converter 102 illustrated inFIG. 1 is about 230 MWe (produced by the generator 110) plus 300 MWe(produced by the generator 150) divided by 1100 MWth (produced thermallyby the inert gas power source 101), which is about 45 to 50%, almostdouble that of a conventional fuel-burning or nuclear-powered powerplant.

Turning now to FIG. 2, illustrated is a diagram of an embodiment of apower generation system. The power generation system is formed with aclosed-loop thermal/electrical power system with a Brayton closed-looppower generator. The elements illustrated in FIG. 2 are not drawn toscale.

Analogous to the power generation system of FIG. 1, the power generationsystem includes the thermal/electrical power converter 102 formed withthe generator 110, the gas turbine 112, and the compressor 114, allmechanically coupled via a rotatable shaft 130. The electrical poweroutput 111 of the generator 110 is coupled through switchgear and theoptional power converter 113 to the ac power grid 106. Descriptions ofremaining elements of the thermal/electrical power converter 102 thatare similar to those describe hereinabove with reference to FIG. 1 willnot be repeated in the interest of brevity.

The high-temperature steam output 142 of heat exchanger 140 is coupledto a high-temperature thermal input of an endothermic process load (alsoreferred to as a “thermally driven process load”) 240, such as achemical processing or refining process. In an embodiment, alow-temperature, liquid-water input 144 of heat exchanger 140 is coupledto a cooling water source 258 such as a river or a screen that mayprovide cooling water at a temperature in the range of 40° F. to 80° F.In an embodiment, the low-temperature, liquid-water input 144 of theheat exchanger 140 is coupled to a low-temperature water output of thethermally driven process load 240. In either case, the low-temperature,liquid-water input 144 can be circulated by a liquid-water pump 260.

The endothermic process load 240 is thus substantially wholly powered bythe power generation system, with exception of the relatively quitesmall power required by the liquid-water pump 260 (or, similarly, byliquid-water pump 160 illustrated in FIG. 1).

The endothermic process load 240, which can be, without limitation, achemical or refining endothermic system, can, in an embodiment, befunctionally incorporated into the process represented by the heatexchanger 140. In such an arrangement, the endothermic process load 240can directly use as a thermal source the high-temperature steam (orother working fluid) provided by the process represented by the heatexchanger 140. The output 142 and the input 144 of the heat exchanger140 could carry a process fluid. In an embodiment, waste heat of theendothermic process load 240 can be directly discharged to a thermalsink, such as a river, or to the atmosphere, with or without a furtherheat exchanger.

The thermally driven process load 240 will generally producehigh-temperature steam that can be cooled and condensed in a heatexchanger (e.g., the heat exchanger/condenser 156 illustrated anddescribed hereinabove with reference to FIG. 1). Alternatively,according to the needs of the thermally driven process load 240, thehigh-temperature steam can be discharged to the atmosphere. Thus, thethermal/electrical power converter 102 can be employed to providehigh-temperature steam or other working fluid to a thermally drivenprocess load 240, and at the same time, produce locally generatedelectricity, all in an environmentally sensitive and safe manner.

A power output of (or a temperature in) the power generation systemillustrated in FIG. 2 can be regulated in a manner analogous to thatdescribed previously hereinabove for the power generation system of FIG.1 via reservoir tank control valves coupled respectively between aninert gas reservoir tank and an input and an output of the compressor114.

Turning now to FIG. 3, illustrated is a diagram of an embodiment of aheat exchanger 140 of a power generation system. The heat exchanger 140is formed with a super-heater heat exchanger 310, a boiler heatexchanger 320, and a water preheater heat exchanger 330 coupled inseries. The super heater heat exchanger 310 is coupled to ahigh-temperature input 129 and a high-temperature steam output 142 ofthe heat exchanger 140. The super-heater heat exchanger 310 isconfigured to extract thermal energy from the high-temperature inert gaspresented at the high-temperature input 129 to super-heated steam at thehigh-temperature steam output 142. An example temperature of the inertgas presented at the high-temperature input 129 is 960° F. In anembodiment, the inert gas is helium. The temperature of the super-heatedsteam produced at the high-temperature steam output 142 is 900° F. orhigher, depending on the efficiency of the super-heater heat exchanger310. The super-heater heat exchanger 310 is thus a gas-to-gas heatexchanger.

A high-temperature, inert gas input of the boiler heat exchanger 320 iscoupled to a reduced temperature, inert gas output of the super-heaterheat exchanger 310. A high-temperature steam output of the boiler heatexchanger 320 is coupled to a steam input of the super-heater heatexchanger 310. An example temperature of fluids at these inputs andoutputs is about 650° F. The boiler heat exchanger 320 is thus agas-to-boiling liquid heat exchanger.

A further-reduced temperature, inert gas input of the pre-heater heatexchanger 330 is coupled to a low-temperature inert gas output of theboiler heat exchanger 320. A high-temperature water output of thepre-heater heat exchanger 330 is coupled to a hot-water input of theboiler heat exchanger 320. An example temperature of fluids at theseinputs and outputs is about 600 to 650° F. A low-temperature,liquid-water input 144 of the heat exchanger 140 is coupled to alow-temperature input of the pre-heater heat exchanger 330, and alow-pressure, low temperature inert gas output of the pre-heater heatexchanger 330 is coupled to a low-pressure output 126 of the heatexchanger 140. An example temperature of fluids at these inputs andoutputs is about 80 to 100° F. The pre-heater exchanger 330 is thus agas-to-liquid heat exchanger.

By constructing the heat exchanger 140 with three heat exchangersforming three heat-exchanger stages as described previously hereinabove,high overall heat-exchanger efficiency can be achieved. A practicalpressure drop of the inert gas helium of about 4% can be achieved ineach of these heat-exchanger stages. The overall pressure drop throughthe heat exchanger assembly would thus be about (1−0.04)³, which isabout 11-12%. The pressure drop of the inert gas flowing through theinert gas power source 101 (see FIG. 1) could be about 5%. The totalpressure drop of the three heat-exchanger stages and the inert gas powersource 101 (about 16%) is made up by a difference in pressure producedby compressor 114 and that absorbed by gas turbine 112 (again, see FIG.1). There is no net loss of energy, because the respectiveinefficiencies due to these pressure drops produce heat that it isultimately absorbed by the thermally driven process load coupled to thehigh-temperature steam output 142 of the heat exchanger 140.

Turning now to FIG. 4, illustrated is an elevation view of an embodimentof an inert gas power source (e.g., a GFR) 101. A GFR is a fast-neutronbreeder reactor operable with a Brayton closed-cycle gas turbine. A GFRemploys helium as a core coolant within a containment vessel 405 capableof sustaining high pressure at high temperature. A reactor core 420 isforce-convection cooled by helium as a working-fluid that is admitted ata low temperature, such as 460° F., at a low-temperature input 422 ofthe inert gas power source 101 and is exhausted at a high temperaturesuch as 1650° F. at a high-temperature output 424 of the inert gas powersource 101. A power level of the reactor core 420 is controlled bycontrol rods 430. Power levels approaching a gigawatt or more areexpected to be achieved in practical designs.

The reactor core 420 operates with a fast-neutron spectrum for efficientutilization of uranium and other fissile fuel sources such as thoriumthat can produce a high gas temperature (e.g., 2000° F. or higher) atthe high-temperature output 424. Helium is a preferred coolant becauseit has a low neutron capture cross-section and does not produce anexplosive gas such as hydrogen, which can be produced by dissociation ofsteam at a high temperature in a water-cooled reactor. Helium has otheradvantages as a coolant in that it does not condense into droplets atlower temperatures in a turbine, which can erode the surface of turbineblades, and does not produce radioactive isotopes in a nuclearenvironment. A GFR has attractive fuel-breeding properties, and isoperable for many years without a need to recharge the fuel.

A new era for standardizing power plant unit production is thus enabledby utilization of a thermal/electrical power converter powered by aninert gas reactor such as a GFR or a VHTR to power a new or existingthermally driven process load. Economically affordable cost to build orrenew a power plant by adopting multiple, standardized, high-efficiencymodifications adds further advantage.

Turning now to FIG. 5, illustrated is a flow diagram of an embodiment ofa method for providing power for a thermally-driven process load. Themethod begins in a start step or module 500. In a step or module 505, aninput of a gas turbine is coupled to a high-temperature output of aninert gas power source. In a step or module 510, a super-heater heatexchanger, a boiler heat exchanger, and a water preheater heat exchangerare coupled in series to form a heat exchanger. In a step or module 515,a low-pressure output of the gas turbine is coupled to ahigh-temperature input of the heat exchanger. In a step or module 520, alow-pressure input of a compressor is coupled to a low-pressure outputof the heat exchanger. In a step or module 525, a high-pressure outputof the compressor is coupled to a low-temperature input of an inert gaspower source. In a step or module 530, a rotatable shaft of thecompressor is mechanically coupled to a rotatable shaft of the gasturbine. In a step or module 535, the rotatable shaft of the gas turbineis mechanically coupled to a rotatable shaft of a generator. In a stepor module 540, a high-temperature steam output of the heat exchanger iscoupled to a high-temperature input of the thermally-driven processload. In a step or module 545, a low-temperature output of thethermally-driven process load is coupled to a low-temperature,liquid-water input of the heat exchanger. In a step or module 550, areservoir tank (an inert gas reservoir tank such as a helium gas tank)is coupled to a low-pressure input of the compressor via a firstreservoir tank control valve and the high-pressure output of thecompressor via a second reservoir tank control valve. The reservoir tankis also coupled to the low-temperature input of the inert gas powersource via a return line between the compressor and the inert gas powersource. In a step or module 555, a power output and/or optionally a gastemperature of inert gas thermal power is controlled with the first andsecond reservoir tank control valves. In a step or module 560, themethod ends.

Although the high-efficiency modifications as discussed herein have beenoriented to a greatly needed, clean overhaul of a depleted, coal firedpower plant, the high-efficiency modifications are equally applicable tosubstantially eliminate the hazards of today's nuclear power plants.This could be accomplished within the context of a modification of thesteam supply to the existing nuclear power plant steam turbinegeneration plant. The water-cooled reactor would be shut down. Thehigh-efficiency modifications to provide a steam generator would beconnected to the steam supply piping coupled to the steam turbine. Forturbine steam supply flow rate and temperature matching, multiplestandard high efficiency inert gas modification units could bemanifolded. This process would be performed following purge of allradioactive water from the generating system including the condenserwater. Through the purging, the remnant hazards of radioactive water arepermanently eliminated.

The prior conventional nuclear power plant would then become safe frommelt-down, explosions, and release of radioactive gases, liquids andparticles. The original turbine/generator, physical, thermal, andelectrical infrastructure may again be retained in service, with anincrease in electrical generating capacity, and with no increase incooling water supply.

Many of the major components of a previously functioning coal orfossil-fuel powered steam power plant including grid connection can bere-used, except the steam generation sub-system, which includes thepreviously used fuel supply and handling, firebox, boiler, andcombustion gas exhaust chimney stacks. A water-cooled nuclear fissionreactor could be similarly replaced.

A number of design variables influence compound plant performance. As anon-limiting example, the following assumptions are made, and computedperformance results are shown in Table I below for a rescued steam plantdesign:

TABLE I An Example Compound System thermal generating capacity of new1100 MWth inert gas reactor original plant electrical capacity 300 MWeoutput from 1500 psi/900° F. input added plant electrical capacity 230MWe total electrical capacity of modified 530 MWe plant thermaldischarge of nuclear reactor negligible to environment reactor inert gasinput pressure 500 psia reactor inert gas output pressure 475 psia corereactor He output temperature 900° C. (1650° F.) gas turbine He outputtemperature 515° C. (960° F.) He compressor efficiency 86% He gasturbine efficiency 88% pressure drop ratio in each of three ∂P/P = .04heat exchangers pressure drop ratio in core reactor ∂P/P = .05compressor pressure ratio 3.2:1 gas turbine pressure ratio 2.7:1He-to-steam mass ratio in heat 1.28 lb He/lb steam exchanger arrangementoverall efficiency of modified, 47% combined plant

As indicated above, the resulting capacity of the modified plant isabout 1.75 times the previously existing capacity with no increasedthermal load on the environment.

In an embodiment, the compressor 114, the gas turbine 112, and thegenerator 110 can be set to operate at a variable speed of rotation.This enables variation and control of the output temperature of the gasturbine gas flow to the high-temperature input 129 to the heat exchanger140.

A unique characteristic of the modifications introduced herein isflexibility to change the helium cycle power output at constanttemperature by changing the helium pressure level within operatinglimits. This can maintain thermal efficiency of the gas turbinegenerator at different power levels. Additionally, this characteristiccould be used to maintain steam temperature at a varying water/steamflow rate, or to vary the steam temperature at the same steam flow rate.Within GFR/VHTR operating pressure and flow limits, plant modificationscoupled with its variable operating characteristic enable application ofa given physical sized high-efficiency power and steam producing unit tobe thermodynamically sized to match a range of steam turbine power plantsizes. By steam output and return pressurized water pipe manifolding ofone or more high efficiency modified gas turbine/steam producing units,a broad range of steam turbine plant sizes can be accommodated.

Thus, a power generation system has been introduced herein. In oneembodiment, the power generation system includes an inert gas thermalpower source, a thermal/electrical power converter and athermally-driven process load. The thermal/electrical power converterincludes a closed-cycle gas turbine engine having a gas turbine with aninert gas input couplable to an inert gas output of the inert gasthermal power source, a compressor, mechanically coupled to the gasturbine, including an inert gas output couplable to an inert gas inputof the inert gas thermal power source, and a generator mechanicallycoupled to the gas turbine. The thermal/electrical power converter alsoincludes a heat exchanger with an input coupled to an inert gas outputof the gas turbine and an inert gas output coupled to an input of thecompressor. The heat exchanger includes a series-coupled super-heaterheat exchanger, a boiler heat exchanger and a water preheater heatexchanger. The thermal/electrical power converter also includes an inertgas reservoir tank coupled to the inert gas input of the compressor viaa reservoir tank control valve and to an inert gas output of thecompressor via another reservoir tank control valve. The reservoir tankcontrol valve and the another reservoir tank control valve areconfigured to regulate a power output of the thermal/electrical powerconverter. The thermally-driven process load includes an input coupledto another output of the heat exchanger and an output coupled to anotherinput of the heat exchanger. The thermally-driven process load ispowered by the thermal/electrical power converter, which in turn ispowered by the inert gas thermal power source. In an embodiment, thethermally-driven process load is wholly powered by thethermal/electrical power converter, which in turn is wholly powered bythe inert gas thermal power source.

Electrical power generation systems may be constrained by an underlyinginefficiency of Carnot-cycle thermal engines (as universally used inelectrical power plants), which depends on a temperature differencebetween a hot source that supplies energy to the plant and a cold-sidethermal sink or cold sink that absorbs remaining energy. The higher theinput temperature, the greater the possible power conversion efficiencyfor a fixed cold-side temperature provided by, for example, a lake or astream. As a result of this observation, additional energy can beobtained from a heat source embodied in a nuclear reactor beyond thatobtained by a cooler fossil fuel burning power plant by utilizing ahigher temperature of a nuclear reactor core, such as 1600° F. or more,as a heat source for a first stage. The cold-side output of the firststage, which might be 900° F., is then used as the thermal input for aconventional power plant. The conventional power plant effectivelybecomes the heat sink for the first stage.

The operating temperature of the nuclear reactor core can besubstantially higher than that produced by a fossil fuel burning powerplant by using an inert gas coolant such as helium to extract thermalenergy from the reactor core. The inert gas coolants typically do notchemically attack the blades of a turbine that converts the thermalenergy produced by the reactor core to a mechanical output. The netresult of using a reactor core as a thermal source cooled by an inertgas is a substantial improvement in plant energy efficiency that enablesadditional useful electrical energy to be produced without increasingthe energy dumped into a lake or stream that acts as the cold-sidethermal sink. The fossil fuel burning power plant may be eliminated. Thelake or stream or other thermal sink is still used to absorb heat from asecond stage, but no additional thermal load is presented to the lake orstream while producing a higher level of electrical power output.

The Carnot efficiency, which presents a maximum theoretical plantefficiency, can be computed using the expression 1−(T_(c)/T_(h)) whereT_(c) is the temperature of the cold sink and T_(h) is the temperatureof the hot source, both measured relative to absolute zero temperature(e.g., in degrees Kelvin or Rankin, not Celsius or Fahrenheit). As thetemperature of the hot source becomes very high, the Carnot efficiencyapproaches unity. Of course, the attainable efficiency in practice isless than that computed by the Carnot expression due to practicalequipment design limitations.

Taking advantage of a large temperature difference between a nuclearreactor core and a thermal sink such as a lake or stream, as introducedherein, a power generation system is formed with a thermal/electricalpower converter that employs helium as a coolant for a nuclear reactorcore. Helium, unlike other reactor coolants such as water, liquidsodium, air, or other inert gases such as argon, doesn't exhibitradioactivity upon exposure to radiation produced in the reactor core.No radioactive byproducts are produced by helium itself, unlike waterand other possible reactor coolants. The nuclear reactor core stillproduces its own spent radioactive fuel, but the absence of radioactiveproducts that are produced when using helium as a coolant providessignificant design and operational advantages. In addition, helium isentirely chemically unreactive with turbine blades, even at quite hightemperatures such as 1600° F. Using steam as a working fluid limitsturbine input temperatures to about 900° F.

Due to its very low atomic weight and its monoatomic gas structure,helium may employ a multi-stage mechanical design for the turbine andcompressor versus a cooling system that employs a higher molecularweight gas such as steam, carbon dioxide, or air. For example, a turbineoperating with helium and operating with a 3:1 pressure ratio betweenits input and output may employ about 20-stage compressor and turbinedesigns. A 20-stage turbine operating with argon and rotating at a samerotational rate could operate with about a 40:1 pressure ratio.

As introduced herein, substantial redesign of conventional turbines andcompressors can be avoided by using, without limitation, argon or amixture of argon and helium as the working fluid in the turbine andcompressor. Helium has a molecular weight of about four. Argon has ahigher molecular weight of about 40 versus about 18 for steam and 29 forair, thereby facilitating the turbine and compressor design. Steam(water) and air, however, produce radioactive byproducts upon exposureto radiation in the nuclear reactor core and, as mentioned above,chemically react with the turbine blades at high temperatures. It iscontemplated that nitrogen as an inert gas can be substituted for theargon.

Thus, a disadvantage of using argon as a coolant/working fluid in thenuclear reactor core is its production of radioactive byproducts uponexposure to radiation in the reactor core. Helium is a desirable reactorcoolant because it does not become radioactive upon exposure to anuclear core and has excellent heat-transfer properties. Argon isdesirable because of its higher atomic weight and associated advantagesrelated to design of turbines and compressors. Neither helium nor argon,being noble gases, is chemically reactive at high temperatures with theturbine blades.

Thus, a thermal/electrical power system is formed with a nuclear reactorcore cooled with helium as a working fluid. Thermal energy is extractedfrom the helium heated in the reactor core employing a counterflow heatexchanger positioned external to the reactor core and acting as athermal source for an electrical power system. The counterflow heatexchanger employs argon or a mixture of argon and helium as the workingfluid on its output side to simplify the design of the compressor andthe turbine. As a result, helium cools the reactor core while notproducing radioactive byproducts and argon, or mixture (which canproduce radioactive byproducts) is not exposed to radiation in the coreof the reactor. In an embodiment, the counterflow heat exchanger employsa mixture of helium and argon as the working fluid on its output side. Amixture of helium and another inert gas such as nitrogen can also beused.

The counterflow heat exchanger extracts heat from the helium heated inthe nuclear reactor core and provides the extracted heat to argon orother inert gas, or to an inert gas mixture. Argon or, alternatively, amixture of helium and argon (or other higher molecular weight inert gas)does not degrade the turbine blades at high temperatures and admits theuse of a turbine that can operate at temperatures higher than those usedin conventional steam-driven power plants. Thus, the thermal input to athermal/electrical power plant is also the heat sink for the first stageof the combined process. The input to the thermal/electrical power plantbecomes both a heat sink for the first stage and a heat source for thesecond stage.

The thermal/electrical power plant is reused with little modificationand power derating as the second stage, and radioactive byproducts areavoided by using helium to cool the nuclear reactor core in the firststage. The first stage produces power that can be added to that producedby the second stage that is already installed. The combined systemproduces about 40 percent more electrical power than the originalconventional power plant with no added thermal burden on a nearby lakeor stream, and no discharge of carbon dioxide and other contaminants tothe atmosphere.

Turning now to FIG. 6, illustrated is a diagram of an embodiment of apower generation system. The power generation system includes two,interdependent, closed-loop thermal/electrical power systems with afirst stage Brayton closed-loop power generation and processing system,and a second stage Rankine closed-loop power processing system. Theelements illustrated in FIG. 6 are not drawn to scale.

Analogous to the power generation system of FIG. 1, the first stage isthe thermal/electrical power converter 102 and the second stage is thepower plant 104. The thermal/electrical power converter 102 is poweredby the inert gas power source 101 (e.g., see FIGS. 1 and 4) via acounterflow heat exchanger 600.

A high-temperature output 424 of the inert gas power source 101 iscoupled to a thermal input 610 of the counterflow heat exchanger 600. Athermal output 620 of the counterflow heat exchanger 600 is coupled tothe input 124 of the gas turbine 112 of the thermal/electrical powerconverter 102. On the return side, the high-pressure output 121 of thecompressor 114 of the thermal/electrical power converter 102 is coupledto an input 625 of the counterflow heat exchanger 600. A low-temperatureoutput 630 of the counterflow heat exchanger 600 is coupled to alow-pressure input 635 of a circulating pump 640 via a filter 645. Ahigh-pressure output 650 of the circulating pump 640 is coupled to alow-temperature input 422 of the inert gas power source 101 via a returnline 122.

The inert gas power source 101 such as a VHTR or a GFR can introducedust particles into the inert gas flow, particularly with a pebble-bedreactor. Over time, dust particles can erode gas turbine and compressorblades, and even inert gas piping at piping bends. To remove such dustparticles from the inert gas flow, the filter 645 can be installedbetween the low-temperature output 630 of the counterflow heat exchanger600 and the low-pressure input 635 of the circulating pump 640, which isa low temperature position to install such a filter 645. In anembodiment, such a filter 645 can have a minimum equivalent reportingvalue (“MERV”) of seven.

A reservoir tank 655 is coupled to the return line 122 via a valving andpumping apparatus 660. The valving and pumping apparatus 660 is employedto maintain a pressure of an inert gas such as helium inside the inertgas power source 101 to regulate a temperature (such as 1600° F.) and/ora pressure (such as a few dozen atmospheres or more) at thehigh-temperature output 424 of the inert gas power source 101 in view ofa fluctuating electrical load on the two-stage power generation system.

The thermal/electrical power converter 102 is assumed herein to beoperable between its input and a combined output that includes theelectrical power output 111 of the generator 110 and a thermal outputbetween a high-temperature steam output 142 and a low-temperature,liquid-water input 144 of the heat exchanger 140 with highly efficientpower conversion. This assumes that the generator 110 is operable withsubstantially 100 percent power conversion efficiency. A practicalgenerator operable to convert mechanical shaft power to an electricaloutput in a power plant can generally achieve a power conversionefficiency in the mid- to high-90 percent range, and the slightlyimperfect power conversion efficiency of such a high-power generator isignored herein. Such mechanical-to-electrical power conversion plantsare not limited by a second-law efficiency constraint imposed by aCarnot cycle. It is contemplated that heat produced in the generator 110by its imperfect power conversion efficiency can be recaptured in thecold-side thermal loop, for instance, before the filter 131.

The high-temperature steam output 142 of the heat exchanger 140 iscoupled to an input 143 of the power plant 104. In an embodiment, thethermal energy produced at the high-temperature steam output 142 of theheat exchanger 140 provides the power input to the power plant 104,which can be an existing, modified steam-driven plant. A high-pressure,cooled-water output 145 of the power plant 104 is coupled to thelow-temperature, liquid-water input 144 of the heat exchanger 140. Thus,substantially the entire thermal output of thermal/electrical powerconverter 102 is supplied to the power plant 104, with possibleexception of the small inefficiency of the generator 110 and modestinefficiency of the counterflow heat exchanger 600. No substantialthermal sink need be coupled to the thermal/electrical power converter102 with exception of modest cooling for the generator 110. In anembodiment, thermal energy obtained from cooling the generator 110 isrecovered at the heat exchanger 140.

Pipeline pressure losses are included in calculating heat exchangerpressure drops for convenience in calculating system performanceevaluations. A small pressure drop at the input side of the heatexchanger 140 does not contribute to system inefficiency. The smallpressure drop of the heat exchanger 140 is simply accommodated byoperating pressure differences between the compressor 114 and the gasturbine 112. Thermal content of heated water or other heated fluid thatmay be employed to cool the generator 110 (or other system elements) maybe employed to preheat the low pressure, cooled inert gas at thehigh-temperature steam output 142 of the heat exchanger 140 before beingsupplied to the compressor 114 to provide a further efficiencyenhancement to the thermal/electrical power converter 102. The powerplant 104 is operable as described previously hereinabove with referenceto FIG. 1. The overall power-conversion efficiency of the powergeneration system illustrated in FIG. 6 is similar to that describedhereinabove with reference to FIG. 1 and won't be repeated in theinterest of brevity.

Turning now to FIG. 7, illustrated is a diagram of an embodiment of apower generation system. The power generation system of FIG. 7 isanalogous to the power generation system of FIG. 6, but more clearlydemonstrates the relationships between the stages thereof. Asillustrated, an output of the thermal/electrical power converter 102(the first stage) is thermally coupled in series to a thermal input ofthe power plant 104. The high-temperature water output 158 of the powerplant 104 is thermally coupled to a cold sink such as a lake or astream. Electrical power outputs of the thermal/electrical powerconverter 102 and the power plant 104 are electrically coupled inparallel as demonstrated by the connection to the power grid 106. Theremaining items illustrated in FIG. 7 have been described previouslyhereinabove and will not be redescribed in the interest of brevity.

Thus, as introduced herein, a counterflow heat exchanger is insertedbetween an inert gas power source employing an inert gas such as heliumand a cascaded arrangement of a thermal/electrical power converter and apower plant. By positioning the counterflow heat exchanger between thehelium-cooled inert gas power source and the cascaded arrangement of thethermal/electrical power converter and the power plant, beneficialthermal and radioactive aspects of the power generation system arerealized. Helium is a desirable coolant for the inert gas power sourcebecause it does not become radioactive upon exposure to a nuclear coreand has excellent heat-transfer properties. Employing a second inert gassuch as argon, an inert gas mixture such as argon and helium, or air (ormixture of air and an inert gas) with a higher molecular weight in thefirst stage of the cascaded arrangement (the thermal/electrical powerconverter) simplifies design of a compressor and turbine. Thearchitecture further allows a reservoir tank arrangement containing theinert gas mixture and coupled to two control valves to control thetemperature and pressure of the inert gas mixture that is dischargedfrom a turbine in the first stage of the cascade arrangement ofthermal/electrical power converter coupled to a generator. The resultenables the temperature of a working fluid fed to the second stage (apower plant) to be controlled.

Turning now to FIG. 8, illustrated is a flow diagram of an embodiment ofa method for providing power for a thermally-driven process load. Themethod begins in a start step or module 805. In a step or module 810, ahigh-temperature output of the inert gas power source employing a firstinert gas such as helium is coupled to a thermal input of thecounterflow heat exchanger. The counterflow heat exchanger is configuredto transfer thermal energy from the inert gas power source to a firststage of the power generation system. In a step or module 815, an inputof a gas turbine of the first stage of the power generation system iscoupled to a thermal output of the counterflow heat exchanger. The firststage of the power generation system conducts a second inert gas such asargon, air or a mixture. In a step or module 820, a super-heater heatexchanger, a boiler heat exchanger, and a water preheater heat exchangerare coupled in series to form another heat exchanger. In a step ormodule 825, a low-pressure output of the gas turbine is coupled to ahigh-temperature input of the another heat exchanger. In a step ormodule 830, a low-pressure input of a compressor is coupled to alow-pressure output of the another heat exchanger.

In a step or module 835, a high-pressure output of the compressor iscoupled to an input of the counterflow heat exchanger. In a step ormodule 840, another output of the counterflow heat exchanger is coupledto a low-pressure input of a circulating pump via a filter. In a step ormodule 845, a high-pressure output of the circulating pump is coupled toa low-temperature input of the inert gas power source via a valving andpumping apparatus and a reservoir tank (an inert gas reservoir tank suchas a helium gas tank). The circulating pump enables an inert gas such ashelium to circulate between the inert gas power source and thecounterflow exchanger. The reservoir tank coupled to the inert gas powersource by the valving and pumping apparatus is configured to regulate atemperature and/or pressure at the output of the inert gas power source.

In a step or module 850, a rotatable shaft of the compressor ismechanically coupled to a rotatable shaft of the gas turbine. In a stepor module 855, the rotatable shaft of the gas turbine is mechanicallycoupled to a rotatable shaft of a generator. In a step or module 860, ahigh-temperature steam output of the another heat exchanger is coupledto a high-temperature input of the thermally-driven process load. In astep or module 865, a low-temperature output of the thermally-drivenprocess load is coupled to a low-temperature, liquid-water input of theanother heat exchanger. In a step or module 870, another reservoir tank(an inert gas reservoir tank such as an argon or mixture gas tank) iscoupled across the compressor via a first reservoir tank control valveand a second reservoir tank control valve. In a step or module 875, apower output and/or optionally a gas temperature of the inert gas powersource is controlled with at least one valve coupled to the reservoirtanks. In a step or module 880, the method ends.

A power generation system and related method of forming and operatingthe same has been introduced herein. In one embodiment, the powergeneration system includes an inert gas power source (101) having aninput (422, 122) and an output (424), and a thermal/electrical powerconverter (102) including a compressor (114) with an output (121)coupled to the input (422, 122) of the inert gas power source (101). Thepower generation system also includes a power plant (104) with an input(143) coupled in series with an output (142) of the thermal/electricalpower converter (102), wherein the thermal/electrical power converter(102) and the power plant (104) are configured to serially convertthermal power produced at the output (424) of the inert gas power source(101) into electricity.

The power generation system may also include an inert gas reservoir tank(116) coupled to an input (123) of the compressor (114) via a reservoirtank control valve (117) and to the output (121) of the compressor (114)via another reservoir tank control valve (118). The reservoir tankcontrol valve (117) and the another reservoir tank control valve (118)are configured to regulate a temperature and/or pressure of the output(142) of the thermal/electrical power converter (102). The powergeneration system may also include a heat exchanger (140) having aninput (129) coupled to an output (128) of a gas turbine, an output (126)coupled to the input (123) of the compressor (114), and the output (142)coupled to the power plant (104). The thermal/electrical power converter(102) and the power plant (104) are thermally coupled in series andelectrically coupled in parallel.

The power generation system may also include a counterflow heatexchanger (600) with an input (610) coupled to the output (424) of theinert gas power source (101), and an output (620) coupled to an input(124) of a gas turbine (112) of the thermal/electrical power converter(102). The inert gas power source (101) provides a first inert gas(e.g., helium) to the input (610) of the counterflow heat exchanger(600) to transfer thermal energy to a second inert gas (e.g., argon or amixture of argon and helium) or air (or a mixture of air and an inertgas) at the output (620) of the counterflow heat exchanger (600). Thesecond inert gas may have an average molecular weight equal to orgreater than an average molecular weight of air.

The power generation system may also include a circulating pump (640)configured to circulate the first inert gas between the inert gas powersource (101) and the counterflow heat exchanger (600). A filter (645) ofthe power generation system is coupled between another output (630) ofthe counterflow heat exchanger (600) and an input (635) of thecirculating pump (640). The power generation system may also includeanother inert gas reservoir tank (655) coupled to the inert gas powersource (101) by a valving and pumping apparatus (660) configured toregulate a temperature and/or pressure at the output (424) of the inertgas power source (101).

As described above, the exemplary embodiment provides both a method andcorresponding systems consisting of various modules providingfunctionality for performing the steps of the method. The modules may beimplemented as hardware, software or combinations thereof. Although theembodiments and its advantages have been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made herein without departing from the conceptual spirit and scopethereof as defined by the appended claims. Also, many of the features,functions, and steps of operating the same may be reordered, omitted,added, etc., and still fall within the broad scope of the variousembodiments.

Moreover, the scope of the various embodiments is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized as well. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A power generation system, comprising: an inertgas power source comprising an input and an output; a thermal/electricalpower converter including a compressor with an output coupled to saidinput of said inert gas power source; a power plant with an inputcoupled in series with an output of said thermal/electrical powerconverter, wherein said thermal/electrical power converter and saidpower plant are configured to serially convert thermal power produced atsaid output of said inert gas power source into electricity; and aninert gas reservoir tank coupled to an input of said compressor via areservoir tank control valve and to said output of said compressor viaanother reservoir tank control valve, said reservoir tank control valveand said another reservoir tank control valve being configured toregulate a temperature of said output of said thermal/electrical powerconverter.
 2. The power generation system as recited in claim 1 furthercomprising a counterflow heat exchanger with an input coupled to saidoutput of said inert gas power source, and an output coupled to an inputof a gas turbine of said thermal/electrical power converter.
 3. Thepower generation system as recited in claim 2 wherein said inert gaspower source provides a first inert gas to said input of saidcounterflow heat exchanger to transfer thermal energy to a second inertgas at said output of said counterflow heat exchanger.
 4. The powergeneration system as recited in claim 3 wherein said first inert gas ishelium and said second inert gas is argon or a mixture of argon andhelium.
 5. The power generation system as recited in claim 3 whereinsaid second inert gas has an average molecular weight equal to orgreater than an average molecular weight of air.
 6. The power generationsystem as recited in claim 2 further comprising a circulating pumpconfigured to circulate a first inert gas between said inert gas powersource and said counterflow heat exchanger.
 7. The power generationsystem as recited in claim 6 further comprising a filter coupled betweenanother output of said counterflow heat exchanger and an input of saidcirculating pump.
 8. The power generation system as recited in claim 1further comprising another inert gas reservoir tank coupled to saidinert gas power source by a valving and pumping apparatus configured toregulate a temperature at said output of said inert gas power source. 9.The power generation system as recited in claim 1 further comprising aheat exchanger having an input coupled to an output of a gas turbine, anoutput coupled to said input of said compressor, and said output coupledto said power plant.
 10. The power generation system as recited in claim1 wherein said thermal/electrical power converter and said power plantare thermally coupled in series and electrically coupled in parallel.11. A method, comprising: providing an inert gas power source comprisingan input and an output; coupling an output of a compressor of athermal/electrical power converter to said input of said inert gas powersource; coupling an output of said thermal/electrical power converter inseries with an input of a power plant, wherein said thermal/electricalpower converter and said power plant are configured to serially convertthermal power produced at said output of said inert gas power sourceinto electricity; and coupling an inert gas reservoir tank to an inputof said compressor via a reservoir tank control valve and to said outputof said compressor via another reservoir tank control valve, saidreservoir tank control valve and said another reservoir tank controlvalve being configured to regulate a temperature of said output of saidthermal/electrical power converter.
 12. The method as recited in claim11 further comprising coupling said output of said inert gas powersource to an input of a counterflow heat exchanger, and coupling aninput of a gas turbine of said thermal/electrical power converter to anoutput of said counterflow heat exchanger.
 13. The method as recited inclaim 12 further comprising providing a first inert gas via said inertgas power source to said input of said counterflow heat exchanger totransfer thermal energy to a second inert gas at said output of saidcounterflow heat exchanger.
 14. The method as recited in claim 13wherein said first inert gas is helium and said second inert gas isargon or a mixture of argon and helium.
 15. The method as recited inclaim 13 wherein said second inert gas has an average molecular weightequal to or greater than an average molecular weight of air.
 16. Themethod as recited in claim 12 further comprising circulating a firstinert gas via a circulating pump between said inert gas power source andsaid counterflow heat exchanger.
 17. The method as recited in claim 16further comprising coupling another output of said counterflow heatexchanger to an input of said circulating pump via a filter.
 18. Themethod as recited in claim 11 further comprising coupling another inertgas reservoir tank to said inert gas power source by a valving andpumping apparatus configured to regulate a temperature at said output ofsaid inert gas power source.
 19. The method as recited in claim 11further comprising: coupling an input of a heat exchanger to an outputof a gas turbine, coupling an output of said heat exchanger to saidinput of said compressor, and coupling said output to said power plant.20. The method as recited in claim 11 wherein said thermal/electricalpower converter and said power plant are thermally coupled in series andelectrically coupled in parallel.